// 实现Base64加密
function base64Encode(str) {
    let base64 = new Base64();
    return base64.encode(str);
}

// 实现Base64解密
function base64Decode(str) {
    let base64 = new Base64();
    return base64.decode(str);
}

// 定义Base64对象
function Base64() {

    // Base64字符集
    const base64Chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

    // 编码函数
    this.encode = function (str) {
        let result = '';
        for (let i = 0; i < str.length; i += 3) {
            let a = str.charCodeAt(i);
            let b = i + 1 < str.length ? str.charCodeAt(i + 1) : 0;
            let c = i + 2 < str.length ? str.charCodeAt(i + 2) : 0;

            let a1 = a >> 2, a2 = ((a & 3) << 4) | (b >> 4), a3 = ((b & 15) << 2) | (c >> 6), a4 = c & 63;

            result += base64Chars[a1] + base64Chars[a2] + (i + 1 < str.length ? base64Chars[a3] : '=') + (i + 2 < str.length ? base64Chars[a4] : '=');
        }
        return result;
    }

    // 解码函数
    this.decode = function (str) {
        let result = '';
        let i = 0;
        while (i < str.length) {
            let a = base64Chars.indexOf(str.charAt(i++));
            let b = base64Chars.indexOf(str.charAt(i++));
            let c = base64Chars.indexOf(str.charAt(i++));
            let d = base64Chars.indexOf(str.charAt(i++));

            let a1 = (a << 2) | (b >> 4);
            let a2 = ((b & 15) << 4) | (c >> 2);
            let a3 = ((c & 3) << 6) | d;

            result += String.fromCharCode(a1);
            if (c != 64) {
                result += String.fromCharCode(a2);
            }
            if (d != 64) {
                result += String.fromCharCode(a3);
            }
        }
        return result;
    }
}

// 向外暴露方法
module.exports = {
    base64Encode: base64Encode,
    base64Decode: base64Decode
}  